US President Barack Obama speaks during a news conference with German Chancellor Angela Merkel at Schloss Herrenhausen in Hanover, Germany, April 24, 2016. [Photo/Agencies]

When Elizabeth Trudeau, director of US State Department Press Office, read a statement on Tuesday about a US Navy surface ship "exercising the right of innocent passage" while transiting near China's Yongshu Reef that day, she said it was to uphold the rights and freedoms of all states under international law and to challenge the excessive maritime claims of some claimants in the South China Sea.

She was soon challenged by an Associated Press reporter about who determines what constitutes an excessive maritime claim. Trudeau, who, like most people, clearly does not understand much of the United Nations Convention on the Law of the Sea, said this is consistent with UNCLOS.

She was then reminded that the US has not ratified UNCLOS, unlike more than 160 other countries. The US' concern is that ratifying the convention would subject it to international laws that would diminish the US' sovereignty on the high seas.

Such hypocrisy aside, the US Navy action reflects the deep-rooted US mentality that it is the self-appointed world's policeman.

It was just like a CNN report earlier this week talking about Russian military presence in Syria. In the end, the reporter quoted a Syrian civilian as saying that peace and stability can only be brought about by Syrian people, not external forces, implying that the Russian forces are not helping.

Yet as anyone who does not have short memory knows too well it was the US and its NATO allies that were the first external forces to become involved in the conflict in Syria, when they supplied arms to rebel groups and when US President Barack Obama said in 2011 that Syrian President Bashar Assad must go. Since their intervention, the Syrian conflict has escalated, causing huge loss of civilian lives, an influx of refugees and the rise of the Islamic State extremist group.

Unlike his predecessors, Obama's rhetoric has been less supportive of US being the self-appointed policeman of the world. In his last State of the Union Address in January, he said, "How do we keep America safe and lead the world without becoming its policeman?"

However, the US' actions in Syria, Libya and now the South China Sea suggest the US still regards itself as far beyond all other nations and international organizations such as the United Nations.

Yes, the world needs a policeman, and it is debatable whether UN can effectively serve that role. But the US' track record in this regard is hardly impeccable. Throughout the past half a century, it has supported and armed many ruthless dictators from Asia to Africa to Latin America. And it has enforced international laws in favor of its security allies and partners, no matter how bad they behave.

We should not forget that both Saddam Hussein and Osama bin Laden were good friends of the US just less than three decades ago.

The fact of the matter is the world is no safer today with the US serving as the world's policeman, or in euphemism, exercising its global leadership.

I am not denying it has played a positive role at times, but the role of world's policeman clearly needs to be kept under scrutiny by the UN and the international community. Otherwise, it invites chaos if every big power appoints themselves as a global or regional policeman.

A Pew Center poll released on May 5 about America's role in the world showed that most Americans say it would be better if the US just dealt with its own problems and let other countries deal with their own problems as best they can, and more people than before say the US should cut back its defense spending.

That is a clear disapproval by American people for the US playing the role of the world's policeman.

The author is deputy editor of China Daily USA. [email protected]